Impacts of climate change on climatic division for double cropping rice in Guangdong Pro-vince, China.

Based on the dataset of air temperature from 86 stations during 1961 to 2016, and DEM data derived from 1:250000 topographic maps, we analyzed the spatial-temporal changes of key climatic factors (safe period for double cropping rice, ≥10 ℃ active accumulated temperature) using the methods of linear regression, accumulative anomaly, and inverse distance weighted interpolation. The impacts of climate change on climatic division for double cropping rice was studied by combining with the changes of key climate factors for the periods of 1961-1990, 1971-2000, 1981-2010, before (1961-1997) and after (1998-2016) climatic mutation. The results showed that spatial distributions of safe period for double cropping rice and ≥10 ℃ active accumulated temperature were different from place to place in Guangdong. Generally, they were more or higher in south than in north part, in plain than in mountain regions. Under the background of global warming, the safe period for double cropping rice and ≥10 ℃ active accumulated tempera-ture showed a significantly increasing trend with the rate of 1.7 d and 43 ℃·d per decade, respectively. All climatic factor had mutation in the year of 1997. According to the climatic conditions of various maturing rice growth and development, climatic zoning for double cropping rice in Guangdong could be divided into three regions: early maturity with early maturity, early maturity with late maturity, late maturity with late maturity. Those regions were distributed in middle-subtropics of northern Guangdong, south-subtropics of middle Guangdong, and north-tropics of southern Guangdong, respectively. Due to the climate change, the area of late maturity with late maturity significantly increased, the area of early maturity with late maturity significantly decreased, and the area of early maturity with early maturity showed no significant change. Relative to that in 1961-1990, the areas of late maturity with late maturity in 1971-2000 and 1981-2010 increased 1.22×10 hm and 2.56×10 hm, respectively, but the area of early maturity with late maturity decreased 1.13×10 hm and 2.56×10 hm, respectively. The area of late maturity with late maturity was more than doubled, but that of early maturity with late maturity decreased about a half after 1997 than that before in Guangdong.